Conventional refrigerating appliances generally employ an HFC (hydrofluorocarbon) refrigerant having a zero-ozone depletion potential as a refrigerant, but in recent years the use of the HFC refrigerant becomes a problem because it has a very large global warming potential. In view of this, a compressor for use with a refrigerant having a small ozone depletion potential and a small global warming potential has been developed. However, the refrigerant having a small global warming potential generally shows poor stability and has a problem in stability and reliability when used in refrigerating cycles such as, for example, room-air conditioners, car-air conditioners, refrigerators or other air conditioners, all of which are predicated on long-term use.
On the other hand, in the refrigerating cycle, the compressor acts to inhale a gas refrigerant vaporized in an evaporator and compress it to a predetermined pressure and, hence, in order to ensure the stability and reliability of the refrigerant, a state of which greatly varies from a low pressure to a high pressure and from a low temperature to a high temperature, sufficient measures must be taken for the compressor.
As shown in FIG. 7, a conventional scroll compressor has a plurality of compression chambers 103 defined between a stationary scroll 101 and an orbiting scroll 102, and an inhaled refrigerant is compressed, utilizing the fact that the compression chambers 103 move while reducing a volume thereof. The refrigerant compressed to a predetermined pressure is discharged to a discharge chamber through a discharge port 104 defined in an end plate of the stationary scroll 101 at a central portion thereof.
In the scroll compressor of the above-described construction, the pressure the compression chambers 103 always undergoes a given process based on a suction pressure and a volumetric change of the compression chambers 103, irrespective of a discharge pressure. Because of this, an excessive pressure increase occurs depending on the timing at which the discharge port 104 communicates with the compression chambers 103 and causes unstable behaviors of the orbiting scroll 102, in which the orbiting scroll 102 is separated from the stationary scroll 101 or conversely, an abnormal pressure acts on the orbiting scroll 102.
In a scroll compressor having symmetrical compression chambers that has been developed to solve this kind of problem, communication holes are provided to respectively communicate the compression chambers in the middle of compression with a rear side of the stationary scroll and with a rear side of the orbiting scroll, and these communication holes leading to the rear sides are located on a central side relative to a communication hole leading to a discharge side, thereby always applying an appropriate pressure to the orbiting scroll (see, for example, Patent Document 1).